Exhaust gas recirculation (EGR) has been used to lower emissions of internal combustion engines. Introducing EGR to engine cylinders can reduce engine pumping losses as well as formation of NOx. In WO2008/127755, a system is described having an EGR passage located downstream of a compressor on the intake side of an engine and upstream of a turbine on the exhaust side of the engine. The reference also describes a catalyst and particulate filter disposed in the exhaust system at a location downstream of the turbine. In one configuration, the reference describes flowing gases from a location downstream of the compressor at the intake side of the engine, to a location in the exhaust system upstream of the catalyst and particulate filter. The method may be useful for regenerating a particulate filter, but engine emissions may increase when the particulate filter is being regenerated.
Recently, direct injection gasoline engines have been shown to improve engine performance and to reduce transient air-fuel disturbances that may be caused by fuel adhering to the intake manifold and ports of an engine. However, at higher engine speeds and higher engine loads, particulates may form in engine exhaust. Under some conditions, formation of the particulates may be related to the short amount of time between when fuel is injected to the cylinder and when combustion is initiated by a spark plug. Specifically, there may be only a short opportunity for the injected fuel to completely vaporize and form a homogeneous mixture before combustion is initiated. If a homogeneous air-fuel mixture is not formed in the cylinder before combustion is initiated, pockets of stratification may form, and soot may be produced by combusting rich areas within the cylinder air-fuel mixture. Particulate filters have been proposed as one way to reduce emissions of soot.
The inventors herein have developed a system for regenerating a particulate filter while engine feed gas emissions are regulated with exhaust gas recirculation. In particular the inventors have developed a system, comprising: an engine having intake and exhaust systems; a particulate filter and a catalyst disposed in said exhaust system, said catalyst located upstream of said particulate filter; a first passage connecting said intake system and said exhaust system, said first passage entering said exhaust system at a location downstream of said catalyst and upstream of said particulate filter; and a controller that adjusts actuators to direct gases from said intake system to said exhaust system by way of said first passage, said controller simultaneously directing exhaust gases from said exhaust system to said intake system by way of a second passage connecting said intake system and said exhaust system.
By simultaneously flowing gases from the exhaust system to the intake system, and from the intake system to a location in an exhaust system downstream of a catalyst and upstream of a particulate filter; engine emissions can be controlled while regenerating a particulate filter. For example, during part-throttle conditions, EGR can be used to reduce engine feed gas NOX emissions. At the same time, pressurized intake gases can be directed to the exhaust system at a location upstream of a particulate filter and downstream of catalyst. In this way, additional oxygen may be supplied to the exhaust system to oxidize material held by the particulate filter while a catalyst located upstream of the particulate filter processes engine feed gases that have lower levels of NOX related to EGR.
The present description may provide several advantages. Specifically, the approach may improve engine emissions by allowing a catalyst to operate in an efficient operating window while at the same time regenerating a particulate filter. Further, the present method allows EGR to flow to the engine while a particulate filter is being regenerated. Further still, the rate of particulate matter oxidation can be regulated by controlling the flow between the intake system and the exhaust system from feedback output from an oxygen sensor located downstream of the particulate filter.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.